direct access to array. TODO: replace with an opIndex and opIndexAssign
peek element at the top of array
pops one item from the stack
pops multiple items from the stack
push an item to the stack and return its position
pushes multiple items to the stack such that the last element is on the top
calls reserve on array
number of stack elements
set the size directly
the top element by reference
Stack data structure wrapper around dynamic D arrays